(精华)2020年9月10日 C#基础知识点 调用动态链接库DLL(调用系统Api和其他语言编写的DLL)

public partial class Program
    {
        static void FileMethod()
        {
            //var fs = new FileOpen("d:\\data.txt");//自定义调用
            var fs = File.Open("data.txt", FileMode.OpenOrCreate);//系统调用
            var bytes = new byte[fs.Length];
            var count = (int)fs.Length;
            var offset = 0;
            while (count > 0)
            {
                var n = fs.Read(bytes, offset, count);
                if (n == 0)
                    break;
                offset += n;
                count -= n;
            }
        }
    }

    public class FileOpen
    {
        public const uint GENERIC_READ = 0x80000000;
        public const uint GENERIC_WRITE = 0x40000000;
        public const uint CREATE_NEW = 1;
        public const uint CREATE_ALWAYS = 2;
        public const uint OPEN_EXISTING = 3;

        // 使用interop调用CreateFile函数有关CreateFile的详细信息请参阅非托管MSDN参考库
        // DllImport调用动态链接库自动寻找windowsAPI kernel32.dll库包含内存管理等
        [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        static extern SafeFileHandle CreateFile(string lpFileName, uint dwDesiredAccess,
            uint dwShareMode, IntPtr lpSecurityAttributes, uint dwCreationDisposition,
            uint dwFlagsAndAttributes, IntPtr hTemplateFile);

        private SafeFileHandle _handleValue;

        public FileOpen(string path)
        {
            Load(path);
        }

        public void Load(string path)
        {
            if (string.IsNullOrEmpty(path))
            {
                throw new ArgumentNullException(nameof(path));
            }

            _handleValue = CreateFile(path, GENERIC_WRITE, 0, IntPtr.Zero, CREATE_ALWAYS, 0, IntPtr.Zero);

            if (_handleValue.IsInvalid)
            {
                Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
            }
        }
    }